The conventional washing apparatuses of this type have been constructed so that the pipe assembly of a pipe to pour the washing liquid in micro wells and a pipe to suck out the remaining liquid from the micro wells is held by means of a holding means. However, the pipe assembly of this type is defective in that since said pipe assembly comprises a pouring pipe and a suction pipe located adjacent to each other and arranged in rows and the pouring pipe and/or suction pipe must be bent in the middle and as is difficult to form and assemble, when such a micro well is of a small diameter (about 6 mm), special attention must be paid so that both pipes should be inserted in the well, and if not the outer end portion of either pipe may be forced out of the well, whereby satisfactory insertion is not attainable, or the washing liquid may fall out of the well. In the conventional apparatus comprising a number of pipe assemblies to wash a number of wells arranged in rows simultaneously as seen especially in the case of the microtiter plate, unless located correctly relative to the holding means, it will not only become more difficult to insert each pipe assembly correctly in each well but also, if inserted, when each pipe assembly is not located uniformly relative to each well, the washing efficiency of each well is different. Accordingly, the conventional apparatus must be said to be defective in that it is not easy to manufacture in order to prevent the occurrence of such disadvantageous and is also inferior in efficiency.